A novel chrysovirus from a clinical isolate of Aspergillus thermomutatus affects sporulation.

A clinical isolate of Aspergillus thermomutatus (Teleomorph: Neosartorya pseudofischeri) was found to contain ~35 nm isometric virus-like particles associated with four double-stranded (ds) RNA segments, each of which coded for a single open reading frame. The longest dsRNA element (3589 nt) encodes a putative RNA-dependent RNA polymerase (1114 aa), the second longest dsRNA element (2772 nt) encodes a coat protein (825 aa), and the other two dsRNAs (2676 nt, 2514 nt) encode hypothetical proteins of 768 aa and 711 aa, respectively. Phylogenetic analysis of the amino acid sequences showed 41-60% similarity to the proteins coded by the dsRNAs of the most closely related virus, Penicillium janczewskii chrysovirus 2, indicating that it is a new species based on the International Committee on Taxonomy of Viruses criteria for the genus Chrysovirus. This is the first virus reported from A. thermomutatus and was tentatively named Aspergillus thermomutatus chrysovirus 1. A virus free line of the fungal isolate, cured by cycloheximide treatment, produced large numbers of conidia but no ascospores at both 20°C and 37°C, whereas the virus infected line produced ten-fold fewer conidia at 20°C and a large number of ascospores at both temperatures. The effects of the virus on fungal sporulation have interesting implications for the spread of the fungus and possible use of the virus as a biological control agent.

The Effect of Aspergillus Thermomutatus Chrysovirus 1 on the Biology of Three Aspergillus Species.

This study determined the effects of Aspergillus thermomutatus chrysovirus 1 (AthCV1), isolated from Aspergillus thermomutatus, on A. fumigatus, A. nidulans and A. niger. Protoplasts of virus-free isolates of A. fumigatus, A. nidulans and A. niger were transfected with purified AthCV1 particles and the phenotype, growth and sporulation of the isogenic AthCV1-free and AthCV1-infected lines assessed at 20 °C and 37 °C and gene expression data collected at 37 °C. AthCV1-free and AthCV1-infected A. fumigatus produced only conidia at both temperatures but more than ten-fold reduced compared to the AthCV1-infected line. Conidiation was also significantly reduced in infected lines of A. nidulans and A. niger at 37 °C. AthCV1-infected lines of A. thermomutatus and A. nidulans produced large numbers of ascospores at both temperatures, whereas the AthCV1-free line of the former did not produce ascospores. AthCV1-infected lines of all species developed sectoring phenotypes with sclerotia produced in aconidial sectors of A. niger at 37 °C. AthCV1 was detected in 18% of sclerotia produced by AthCV1-infected A. niger and 31% of ascospores from AthCV1-infected A. nidulans. Transcriptome analysis of the naturally AthCV1-infected A. thermomutatus and the three AthCV1-transfected Aspergillus species showed altered gene expression as a result of AthCV1-infection. The results demonstrate that AthCV1 can infect a range of Aspergillus species resulting in reduced sporulation, a potentially useful attribute for a biological control agent.